Showing papers in "International journal of ambient energy in 1997"

Exergeo-economic performance bound and optimisation criteria for heat engines

Abstract: SYNOPSIS Finite-time thermodynamics and exergeoeconomics are combined to form a new analysis method called finite-time exergeoeconomics in this paper. The optimal thermal efficiency and profit rate holographic spectrum for the heat engine is derived. The derivation is used to obtain the efficiency bound at maximum profit rate and the optimisation criteria for selecting thermodynamic parameters of the heat engine cycles. The results provide a solid theoretical basis for design and evaluation of practice heat engines.

Heat pump performance with internal heat leak

Abstract: SYNOPSIS Influence of internal heat leak on the optimal performance of a heat pump is examined in this paper. This is done by adding a heat leak term into an endoreversible heat pump. The relation between optimal heating load and coefficients of performance (COP) for a steady-state irreversible heat pump is derived. The performance characteristics of the irreversible heat pump is found to be deeply affected by the rate of heat leak. This model allows a more reasonable prediction in the performance of an actual heat pump.

The effect of regenerative losses on the efficiency of a Stirling heat engine at maximum power output

Abstract: SYNOPSIS A more realistic cycle model is established for discussing the performance of the Stirling heat engine with regenerative losses. The power output is adopted as an objective function for optimisation. The maximum power output and the corresponding efficiency of the Stirling heat engine are derived. The effect of regenerative losses on the efficiency at maximum power output is expounded. The times of four processes in the Stirling cycle are allotted optimally. Some new conclusions are obtained.

Inverted obsorber solar concentrators for rural applications.

Abstract: SYNOPSIS Design issues for compound parabolic concentrators for rural applications are addressed. Novel uses of asymmetric inverted absorber compound parabolic concentrators in air heating, water heating, distillation and cooking are described.

On the development of a reliability based optimal renewable energy model for the sustainable energy scene in India

Abstract: Sustainable Energy Development Planning has been the thrust area in developing countries like India. An Optimal Renewable Energy Model (OREM) with Reliability constraint which minimises the cost/efficiency ratio has been developed. The other constraints included in the model are social acceptance, resource limitation, demand and reliability factors. Thirty eight different renewable energy options are considered in the model. The OREM gives the allocation of renewable energy sources for lighting, cooking, pumping, heating, cooling and transportation end-uses for the year 2020-21 in India. For sustainable energy, the reliability of renewable energy systems have to be considered. In this paper, a detailed study has been made to analyse the reliability of a 15 kW solar photovoltaic system, which will be used in one of the constraint equations of the model. Reliability analysis reveals that there were no technical failures in the photovoltaic devices. But the power conversion accessories, such as the inverter and output contactor experienced failure rates of 1.48 x 10 -4 /hour and 1.67 x 10 -4 /hour respectively, resulting in poor reliability of the system. The reliability factor of the photovoltaic system is found to be 0.2 at 5000 hours. The fault analysis by Pareto diagram reveals that by eliminating the system component failures, the reliability factor can be improved to the factor of 0.67. As far as the solar PV is concerned, the model (OREM) selects solar PV for lighting to an extent of 0.5198 x 10 15 kJ and for pumping 1.2084 x 10 15 kJ.

Box type solar cooker vs other options for domestic cooking: A financial evaluation

Abstract: SYNOPSIS A box-type solar cooker is a simple device for harnessing solar energy for cooking. The large scale utilisation of solar cookers would depend on its financial performance vis-a-vis other resource-technology combinations for cooking. To facilitate comparison of the financial attractiveness of a solar cooker with other alternatives for domestic cooking, the cost incurred on cooking a given meal and the cost per unit of useful energy delivered by various resource-technology combinations have been estimated in the present work. The sensitivity of these figures of merit with respect to the possible uncertainties in the values of input parameters has also been studied.

Do sunspaces work in Scotland ? Lessons learnt from a CEC solar energy demonstration project in Glasgow

Abstract: SYNOPSIS The paper examines the extent to which user's intervention may compromise the thermal performance of small sunspaces in the context of a Solar Energy Demonstration Project at Easthall in Glasgow (55°52′N), which was monitored from September 1992 to May 1994. Results indicate a tendency to close down windows etc, late in autumn and open them up early in spring relative to heat demand. In other words a user-driven energy load due to ventilation is higher in autumn and spring than in the central winter period. However, effective rate of ventilation, taking account of the preheat effect of the glazed spaces, is found to be more steady over an entire heating season. Thus, inclusion of glazed buffers has been shown to lessen the thermal burden of window opening in autumn and spring; while saving in winter due to preheated air for ventilation tends to be slightly higher than predicted. Results also indicate that amount and frequency of opening/ventilation relates to specific social and occupancy charact...

Solar cooker use in Delhi: pilot survey of urban households

Abstract: SYNOPSIS The objectives, methodology and results of a pilot survey of urban households using box type solar cookers in Delhi are briefly described. Also included are the suggestions of the users for improving the acceptability of the solar cookers.

Energy conservation through hybrid air-conditioning cycles: computer modeling studies

Abstract: SYNOPSIS In this paper the authors have presented a review, analysis and computer modelling of desiccant based hybrid air-conditioning (A/C) cycles for typical hot and humid conditions. Three hybrid cycles based on solid desiccant dehumidifier (viz. ventilation/condenser, recirculation/condenser and ventilation/heat exchanger cycles) have been evaluated and compared in performance with a conventional vapour compression A/C system. Computer modelling and analysis is based on dehumidifier performance data and the air psychrometric properties data correlations. Typical performance results in parametric variations for less and more humid conditions prevailing in Indian cities are presented. It is found that there is considerable scope for energy savings and improvement in the COP with hybrid A/C over the conventional vapour compresion cycle and desiccant cooling cycle alone for high latent heat load conditions.

Sensitivity analysis of a modified energy model

Abstract: SYNOPSIS Sensitivity analysis is carried out to validate model formulation. A modified model has been developed to predict the future energy requirement of coal, oil and electricity considering price, income, technological and environmental factors. The impact and sensitivity of the independent variables on the dependent variable are analysed. The error distribution pattern in the modified model as compared to a conventional time series model indicated the absence of clusters. The residual plot of the modified model showed no distinct pattern of variation. The percentage variation of error in the conventional time series model for coal and oil ranges from −20% to + 20%, while for electricity it ranges from −80% to + 20%. However, in the case of the modified model the percentage variation in error is greatly reduced—for coal it ranges from −0.25% to + 0.15%, for oil −0.6% to + 0.6% and for electricity it ranges from −10% to + 10%. The upper and lower limit consumption levels at 95% confidence is determined...

Enhancement in daily yield due to regenerative effect in solar distillation

Abstract: SYNOPSIS In this communication, an energy balance equation in terms of design and climatic parameters has been written for each component of a regenerative active solar distillation system. An analytical expression for the water and the condensing cover temperatures, the hourly yield and the flowing water temperature has been derived. Numerical computations have been carried out for a typical day in Delhi and it has been inferred that the daily output is increased significantly due to nocturnal production of distilled water.

Energy saving potential integrating multi-stage evaporative technology in HVAC systems for Italian climate

Abstract: SYNOPSIS Evaporative cooling, extensively used in dry climates, can be justified in wetter areas by integration into HVAC systems; in this way the saving-energy technique will not always replace mechanical cooling, but has to be integrated with commonly employed equipment. In this paper Test Reference Year (TRY) data for Italy were processed to estimate using potential of multistage integrated evaporative HVAC systems. Specific humidity and wet-bulb temperature were computed to define five regions for external air, and then to evaluate hours per year and relative energy saving for each of these regions and Italian climatic areas. The systems subjected to comparison were a multi-stage evaporative—direct, indirect and mechanical—and a traditional mechanical one; both all air, single duct, single zone, constant volume systems with wet-bulb economizer. The method of analysis is based on a strongly simplified approach. It is not intended as a substitute for accurate modelling schemes to simulate building and s...

The performance of atria in two school buildings

Abstract: SYNOPSIS Atria have become popular additions to many building types in recent years. There is a common misconception that they will automatically result in lower energy consumption, but this is not necessarily the case. Only when designed and used in an appropriate way will atria contribute to energy conservation. In this paper the performance of two school buildings, one incorporating a heated atrium, the other an unheated atrium, was studied. Comparisons between their performance were made with respect to thermal comfort, heating costs, overheating and daylighting. While heating the atrium incurred a cost penalty, it resulted in comfortable conditions in the space for a greater proportion of the time in winter, and consequently created a more useful space. In summer months overheating was likely unless an area of opening vents the equivalent of 10% or more of the floor area is provided in the atrium roof.

An analysis of next generation building energy simulation tools

Abstract: SYNOPSIS Comprehensive software programs to simulate building energy performances in dynamic conditions are available today for professional purposes. In fact their modern releases are characterised by easy management and by the use of common personal computers. But, in spite of their better precision than simplified steady-state methods, many designers and even various standards, continue to prefer traditional simplified procedures. The possibilities and limits of new transient simulation software packages are investigated. This analysis starts from the results obtained, in some typical application cases, from the use of the two famous programs DOE and BLAST.

Effect of seasonal variation on the performance of a solar water pump

Abstract: SYNOPSIS A brief description of the operation and analysis of a solar water pump is given. The performance of the pump is studied for various solar radiation intensities and ambient temperatures, so that a clear picture on the year-round performance of the pump emerges. The prediction reveals that the number of cycles and the overall efficiency increases with an increase in solar radiation intensity, whereas, with the increase in ambient temperature, the number of cycles initially increases with the temperature up to 30°C and decreases thereafter.

Energy conservation strategies for school buildings in Riyadh

Abstract: SYNOPSIS Although the Kingdom of Saudi Arabia is one of the main oil producing countries, yet the latest five year development plan calls for energy conservation [1]. Due to the expansion of the Saudi economy which is reflected by the challenging and ambitious development in various sectors such as housing, health, industry, agriculture, education etc, the consumption of electric energy experienced a sharp increase during the last twenty years. Electric energy consumption in the central region of Saudi Arabia increased from 4,236,000 MWh in 1981 to 12,996,000 MWh in 1988. Since 1983 the Ministry of Education started implementing various strategies to conserve energy consumption by school buildings. In the 1990s more attention is geared towards improving the U-value of the external envelope through the use of hollow blocks and thermal insulation. This study is an attempt to investigate the effectiveness of the use of thermal insulation and hollow blocks in reducing energy consumption. This is conducted by ...

Applications of open circuit voltage decay technique for the characterisation of photovoltaic devices

Abstract: SYNOPSIS Theoretical and experimental investigations have been carried out upon the applications of the open-circuit voltage decay technique for the characterisation of a large spectrum of photovoltaic cells. The investigated samples are either locally fabricated or commercially available. The study clearly showed the effects of base resistivity value, manufacturing technique, as well as the nuclear radiation on the cells performance.

Parametric study of evaporative heat transfer coefficient in solar distillation

Abstract: SYNOPSIS In this communication, an attempt has been made to study the effect of absorptivity, water depth and bottom heat loss coefficient on the evaporative heat transfer coefficient. The variation of hourly and daily yield with basic variable parameters has been studied. Numerical computations have been carried out for a typical day of Delhi climate. On the basis of numerical results, it is observed that the evaporative heat transfer is a strong function of water depth and absorptivity of the basin as expected.

Analysis and performance evaluation of a cavity roof over a non air-conditioned building

Abstract: SYNOPSIS The roof as a major heat gain source has been analysed. A cavity roof system has been proposed to reduce the heat gain through the roof and a time dependent analysis carried out to model a non air-conditioned room with such a roof. Parametric studies on the effect of the depth of the cavity from the roof-top surface and the thickness of the air cavity have been carried out. The results presented are found to be valuable aids for passive roof design.

The equivalent cycles of an n-stage irreversible combined refrigeration system

Abstract: An irreversible cycle model is used to investigate the performance of an n-stage combined refrigeration system affected by the irreversibility of finite-rate heat transfer and the internal dissipation of the working fluid. Some reasonable parameters are introduced so that the optimal performance of the irreversible combined refrigeration system may be directly derived by an equivalent simplified cycle model. The optimal relation between the coefficient of performance and the specific cooling load of the system is obtained. The optimal combined conditions between two adjacent irreversible cycles in the system, i.e. the optimal ratios of the temperatures of the working fluids in the heat-transfer processes and the optimal distribution of the heat-transfer areas of the heat exchangers in the system, are determined. The results obtained here are general and useful. They may be used to discuss the optimal performance of an arbitrary-stage irreversible and endoreversible combined refrigeration system. Moreover, it is pointed out that the optimal performance of an arbitrary-stage irreversible and endoreversible combined heat pump system may also be derived from the cycle model.

A renewable energy strategy for the UK

Abstract: The case for a renewable energy strategy which helps sustain life, peace and certain development, is argued, based on the premise that: Fossil fuel reserves are limited to perhaps the next generation: That burning fossil and nuclear fuels causes pollution with potentially catastrophic biological and geophysical consequences: and That conflict may arise over scarcity of fossil fuels and selective ownership of nuclear power The relative capacities, social and environmental benefits and costs of the alternatives are compared What architects and engineers might do to promote renewables is proposed

An innovative power pack and motor for a compressed air car of practical performance

Abstract: SYNOPSIS Much more attention is now being paid to local air pollution levels in Europe and America, led by the California Air Resources Board (CARB) who have pronounced that a given percentage of cars sold in that State must be zero emission by a certain date [1]. The obvious contender to fulfil such a requirement is the electric driven vehicle, but manufacturers are having problems producing a reliable battery of sufficient energy density. Do compressed air driven cars represent a viable alternative? Their advantage is the long life of the power pack and the relatively high speed recharging, which must be set against their greater capital cost. The authors show that the pneumatic car can certainly equal the performance of electric transportation when use is made of modern materials and energy recovery through the utilisation of heat pipes, and conclude that they are indeed worthy of further investigation.